Read the following excerpt. I am certainly no chemist, but the
explanation of the difference between the Ionic and Metallic bond may be
the key to the distinction you are trying to make.
(The colloids which we are interested in would consist of groups of
metallically bonded silver atoms, I would think...)
Dan
http://www.answers.com/topic/chemical-bond
CHEMICAL BOND, mechanism whereby atoms combine to form molecules. There
is a chemical bond between two atoms or groups of atoms when the forces
acting between them are strong enough to lead to the formation of an
aggregate with sufficient stability to be regarded as an independent
species. The number of bonds an atom forms corresponds to its valence.
The amount of energy required to break a bond and produce neutral atoms
is called the bond energy. All bonds arise from the attraction of unlike
charges according to Coulomb's law; however, depending on the atoms
involved, this force manifests itself in quite different ways. The
principal types of chemical bond are the ionic, covalent, metallic, and
hydrogen bonds. The ionic and covalent bonds are idealized cases,
however; most bonds are of an intermediate type.
The Ionic Bond
The ionic bond results from the attraction of oppositely charged ions.
The atoms of metallic elements, e.g., those of sodium, lose their outer
electrons easily, while the atoms of nonmetals, e.g., those of chlorine,
tend to gain electrons. The highly stable ions that result retain their
individual structures as they approach one another to form a stable
molecule or crystal. In an ionic crystal like sodium chloride, no
discrete diatomic molecules exist; rather, the crystal is composed of
independent Na+ and Cl− ions, each of which is attracted to neighboring
ions of the opposite charge. Thus the entire crystal is a single giant
molecule.
The Covalent Bond
A single covalent bond is created when two atoms share a pair of
electrons. There is no net charge on either atom; the attractive force
is produced by interaction of the electron pair with the nuclei of both
atoms. If the atoms share more than two electrons, double and triple
bonds are formed, because each shared pair produces its own bond. By
sharing their electrons, both atoms are able to achieve a highly stable
electron configuration corresponding to that of an inert gas. For
example, in methane (CH4), carbon shares an electron pair with each
hydrogen atom; the total number of electrons shared by carbon is eight,
which corresponds to the number of electrons in the outer shell of neon;
each hydrogen shares two electrons, which corresponds to the electron
configuration of helium.
In most covalent bonds, each atom contributes one electron to the shared
pair. In certain cases, however, both electrons come from the same atom.
As a result, the bond has a partly ionic character and is called a
coordinate link. Actually, the only purely covalent bond is that between
two identical atoms.
Covalent bonds are of particular importance in organic chemistry because
of the ability of the carbon atom to form four covalent bonds. These
bonds are oriented in definite directions in space, giving rise to the
complex geometry of organic molecules. If all four bonds are single, as
in methane, the shape of the molecule is that of a tetrahedron. The
importance of shared electron pairs was first realized by the American
chemist G. N. Lewis (1916), who pointed out that very few stable
molecules exist in which the total number of electrons is odd. His octet
rule allows chemists to predict the most probable bond structure and
charge distribution for molecules and ions. With the advent of quantum
mechanics, it was realized that the electrons in a shared pair must have
opposite spin, as required by the Pauli exclusion principle. The
molecular orbital theory was developed to predict the exact distribution
of the electron density in various molecular structures. The American
chemist Linus Pauling introduced the concept of resonance to explain how
stability is achieved when more than one reasonable molecular structure
is possible: the actual molecule is a coherent mixture of the two
structures.
Metallic and Hydrogen Bonds
Unlike the ionic and covalent bonds, which are found in a great variety
of molecules, the metallic and hydrogen bonds are highly specialized.
The metallic bond is responsible for the crystalline structure of pure
metals. This bond cannot be ionic because all the atoms are identical,
nor can it be covalent, in the ordinary sense, because there are too few
valence electrons to be shared in pairs among neighboring atoms.
Instead, the valence electrons are shared collectively by all the atoms
in the crystal. The electrons behave like a free gas moving within the
lattice of fixed, positive ionic cores. The extreme mobility of the
electrons in a metal explains its high thermal and electrical conductivity.
Hydrogen bonding is a strong electrostatic attraction between two
independent polar molecules, i.e., molecules in which the charges are
unevenly distributed, usually containing nitrogen, oxygen, or fluorine.
These elements have strong electron-attracting power, and the hydrogen
atom serves as a bridge between them. The hydrogen bond, which plays an
important role in molecular biology, is much weaker than the ionic or
covalent bonds. It is responsible for the structure of ice.
Bibliography
See L. Pauling, The Nature of the Chemical Bond (3d ed. 1960); A. L.
Companion, Chemical Bonding (2d ed. 1979).
Subject: CS>Ionic vs Particulate
From: Marshall Dudley <mdud...@king-cart.com
Date: Fri, 23 Dec 2005 12:15:46 -0500
To: silver-list@eskimo.com
My decision to ask the definition of ionic in the sci.chem newsgroup
does not seem to have worked out as well as I had hoped. Initially
there was confirmation that the silver oxide/hydroxide is ionic and that
the silver crystals were particulate with a charge but not ionic. Then
other scientists/chemists chimed in and said that the particulate could
be called ionic, and even went as far as to say that if you rub a
diamond on silk and charge it up, it could be called an ion! Also one
indicated that radicals are ions, but not molecules, but another one
said that radicals are molecules, that a molecule does not have to be
neutral.
How the heck can we agree on terms if the professional chemists and
scientists cannot agree on the terms? After one of them suggested that
we use the term "molecular ion" to describe the dissociated salts of
anything, including silver another researcher chimed in last night and
said that "molecular ion" is already used "in mass spectrometry for the
molecule that has acquired a +1 charge and has not been fragmented.
Also called parent peak."
So I am still somewhat at a loss here as to what terminology to use to
definitively separate a molecular silver ion from a suspended silver
crystal. I still like the "molecular ion", but maybe another good term
would be a "disassociated ion". There is obviously a difference between
the disassociated ion of what we call ionic silver, and the particulate
portion of EIS.This is easily proven with both a laser as well as by
adding salt and seeing that the former falls out and the latter does
not. The difference is like the difference in salt water, and a diamond
that has been charged up. The disassociated ion is very reactive, and
the diamond is very stable.
Any other ideas?
Marshall
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